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Android APIs
public class

EdgeEffect

extends Object
java.lang.Object
   ↳ android.widget.EdgeEffect

Class Overview

This class performs the graphical effect used at the edges of scrollable widgets when the user scrolls beyond the content bounds in 2D space.

EdgeEffect is stateful. Custom widgets using EdgeEffect should create an instance for each edge that should show the effect, feed it input data using the methods onAbsorb(int) , onPull(float) , and onRelease() , and draw the effect using draw(Canvas) in the widget's overridden draw(Canvas) method. If isFinished() returns false after drawing, the edge effect's animation is not yet complete and the widget should schedule another drawing pass to continue the animation.

When drawing, widgets should draw their main content and child views first, usually by invoking super.draw(canvas) from an overridden draw method. (This will invoke onDraw and dispatch drawing to child views as needed.) The edge effect may then be drawn on top of the view's content using the draw(Canvas) method.

Summary

Public Constructors
EdgeEffect ( Context context)
Construct a new EdgeEffect with a theme appropriate for the provided context.
Public Methods
boolean draw ( Canvas canvas)
Draw into the provided canvas.
void finish ()
Immediately finish the current animation.
boolean isFinished ()
Reports if this EdgeEffect's animation is finished.
void onAbsorb (int velocity)
Call when the effect absorbs an impact at the given velocity.
void onPull (float deltaDistance)
A view should call this when content is pulled away from an edge by the user.
void onRelease ()
Call when the object is released after being pulled.
void setSize (int width, int height)
Set the size of this edge effect in pixels.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public EdgeEffect ( Context context)

Construct a new EdgeEffect with a theme appropriate for the provided context.

Parameters
context Context used to provide theming and resource information for the EdgeEffect

Public Methods

public boolean draw ( Canvas canvas)

Draw into the provided canvas. Assumes that the canvas has been rotated accordingly and the size has been set. The effect will be drawn the full width of X=0 to X=width, beginning from Y=0 and extending to some factor < 1.f of height.

Parameters
canvas Canvas to draw into
Returns
  • true if drawing should continue beyond this frame to continue the animation

public void finish ()

Immediately finish the current animation. After this call isFinished() will return true.

public boolean isFinished ()

Reports if this EdgeEffect's animation is finished. If this method returns false after a call to draw(Canvas) the host widget should schedule another drawing pass to continue the animation.

Returns
  • true if animation is finished, false if drawing should continue on the next frame.

public void onAbsorb (int velocity)

Call when the effect absorbs an impact at the given velocity. Used when a fling reaches the scroll boundary.

When using a Scroller or OverScroller , the method getCurrVelocity will provide a reasonable approximation to use here.

Parameters
velocity Velocity at impact in pixels per second.

public void onPull (float deltaDistance)

A view should call this when content is pulled away from an edge by the user. This will update the state of the current visual effect and its associated animation. The host view should always invalidate() after this and draw the results accordingly.

Parameters
deltaDistance Change in distance since the last call. Values may be 0 (no change) to 1.f (full length of the view) or negative values to express change back toward the edge reached to initiate the effect.

public void onRelease ()

Call when the object is released after being pulled. This will begin the "decay" phase of the effect. After calling this method the host view should invalidate() and thereby draw the results accordingly.

public void setSize (int width, int height)

Set the size of this edge effect in pixels.

Parameters
width Effect width in pixels
height Effect height in pixels